The present invention relates to a regenerative air preheater having improved insulation between the combustion chamber and checker shaft of the regenerative air preheater.
A typical regenerative air preheater includes a masonry casing having therein a combustion chamber and a checker shaft set with checker bricks, and a separating wall between the combustion chamber and the checker shaft. During operation of the internal shaft regenerative air preheater, considerable temperature differences exist between the combustion chamber side and the checker shaft side of the separating wall, particularly in the lower portion of the separating wall. As a result of such temperature differences, and of the varying expansion of the fireproof stone or brick material of the separating wall, the wall has a tendency to lean toward the colder side, i.e., the checker shaft side, due to the phenomenon known as the "bimetallic effect". This results in stresses which cause cracks and disintegration of the stone or bricks of the separating wall, as well as in the anchoring bricks attaching the separating wall to the casing wall of the regenerative air preheater. This in turn can result in leaks between the combustion chamber and the checker shaft.
Previous attempts to prevent these destructive and disadvantageous occurrences in regenerative air preheaters used to produce hot wind or blast temperatures up to 1300.degree. C. are known, for example, from West German DT-AS 19 38 432. Such previous attempts consist essentially in dividing the separating wall and the casing wall in the area of the combustion chamber into several vertical stone or brick layers with partitions present at least in the cold state of the preheater and to provide an insulation layer consisting of insulation stones or bricks on the side of the partitions in the area opposite to the combustion chamber.
Such attempts involving the placing of a separating wall layer of insulating stones or bricks on the checker shaft side of the separating wall have not had the effect that was desired, since the insulation stones have a high porosity and are relatively mechanically weak. The relatively high temperature gradient across the insulating stones results in high expansion on one side thereof, and this results in a considerable degree of internal tension within the insulating stones. Thus, the insulating stones become destroyed after a relatively short period of time.
If a separating wall layer consisting of insulating stones is packed between two hard stone wall layers, the result is a natural mechanical weakening of the overall separating wall. Additionally, the hard stone layer on the checker shaft side remains considerably cooler and expands less than the section of the casing wall next to the combustion chamber in which it is anchored. This results in the anchors being subjected to the destructive forces of expansion.
It is furthermore known from the above mentioned DT-AS 19 38 432 to provide a metal plate of heat resistant steel in the separating wall, which metal plate even after long periods of use maintains the separating wall in a gastight condition.